Light emitting device

ABSTRACT

A light emitting device and electronic equipment having a long life at a low electric power consumption are provided. A hole transporting region composed of a hole transporting material, an electron transporting region composed of an electron transporting material, and a mixture region in which both the hole transporting material and the electron transporting material are mixed at a fixed ratio are formed within an organic compound film. Regions having a concentration gradient are formed between the mixture region and carrier transporting regions until the fixed ratio is achieved. In addition, by doping a light emitting material into the mixture region, functions of hole transportation, electron transportation, and light emission can be respectively expressed while all of the interfaces existing between layers of a conventional lamination structure are removed. Organic light emitting elements having low electric power consumption and a long life can thus be provided, and light emitting devices and electronic equipment can be manufactured using the organic light emitting elements.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a light emitting device using anorganic light emitting element having an anode, a cathode, and a filmcontaining an organic compound in which light emission can be obtainedby applying an electric field (hereafter referred to as an “organiccompound film”). In particular, the present invention relates to a lightemitting device using organic light emitting elements having a drivervoltage that is lower than a conventional driver voltage and having along life. Note that the term light emitting device within thisspecification indicates image display devices or light emitting devicesusing organic light emitting elements as light emitting elements.Further, modules in which a connector, for example, an anisotropicconductive film (flexible printed circuit, FPC), a TAB (tape automatedbonding) tape, or a TCP (tape carrier package) is attached to organiclight emitting elements, modules in which a printed-wiring board isprovided on the tip of the TAB tape or the TCP, and modules in which anIC (integrated circuit) is directly mounted to the organic lightemitting elements by a COG (chip on glass) method are all included inthe category of the light emitting devices.

[0003] 2. Description of the Related Art

[0004] Organic light emitting elements are elements which emit light bythe application of an electric field. The light emitting mechanism isone in which electrons injected from a cathode recombine within anorganic compound film with holes injected from an anode, formingexcitation state molecules (hereafter referred to as “molecularexcitons”), by the application of a voltage between the electrodessandwiching the organic compound film. Energy is released when themolecular excitons return to a base sate, thereby emitting light.

[0005] Note that it is possible for the molecular excitons formed by theorganic compound to be in a singlet excitation state or in a tripletexcitation state, and both cases in which either excitation state maycontribute to the emission of light are included within thisspecification.

[0006] The organic compound film is normally formed by a thin filmhaving a thickness less than 1 μm for these types of organic lightemitting elements. Further, organic light emitting elements are selflight emitting elements in which light is emitted by the organiccompound films themselves, and therefore a back light like that is usedin a conventional liquid crystal display is not necessary. Consequently,the ability to manufacture the organic light emitting elements that areextremely thin and light is a big advantage.

[0007] Furthermore, the amount of time from the injection of a carrieruntil recombination in an organic compound film having a thickness onthe order of 100 to 200 nm, for example, is on the order of several tensof nanoseconds when considering carrier mobility of the organic compoundfilm, and even in a case of including a process from when the carrierrecombines until light is emitted, the light emission can be reachedwithin one microsecond. Therefore, it is one of the characteristics thatlight emitting elements have an extremely fast response speed.

[0008] In addition, drive using a direct current voltage is possiblebecause the organic light emitting elements are light emitting elementsof a carrier injecting type, and therefore it is difficult for noise todevelop. With regard to a driver voltage, it has been reported(reference 1: Tang, C. W., and VanSlyke, S. A., “OrganicElectroluminescent Diodes”, Applied Physics Letters, Vol. 51, No. 12,pp. 913-915 (1987)) that a sufficient brightness of 100 cd/m² at 5.5 Vwas achieved by first taking an extremely thin film of an organiccompound with a uniform film thickness on the order of 100 nm, selectingan electrode material so as to make a carrier injection barrier of theorganic compound film smaller, and in addition, introducing aheterostructure (two layer structure).

[0009] Organic light emitting elements are therefore under the spotlightas display elements for next generation flat panel display elements dueto their thin size, light weight, high speed response, and dclow-voltage drive. Furthermore, the organic light emitting elements areof a self light emitting type and have a wide field of view, andtherefore their visibility is comparatively good and they are consideredto be effective as elements used in the display screens of portabledevices.

[0010] An Mg:Ag alloy having a low work coefficient and which isrelatively stable is used in the cathode as a method of making thecarrier injection barrier with respect to the organic compound filmsmaller, thereby increasing the electron injection properties, in theorganic light emitting elements shown in reference 1. It is thuspossible to inject a large amount of carrier into the organic compoundfilm.

[0011] In addition, applying a single heterostructure in which a holetransporting layer formed of an aromatic diamine compound and anelectron transporting and light emitting layer formed oftris-(8-quinolinolate)-aluminum (hereafter referred to as “Alq₃”) arelaminated as the organic compound film remarkably increases theefficiency of the recombination property of the carrier. This will beexplained as follows.

[0012] For example, if the organic light emitting elements have only asingle layer of Alq₃, then almost all electrons injected from thecathode will reach the anode without recombining with holes because Alq₃has electron transporting properties, and the efficiency of lightemission is extremely bad. That is, in order to make the efficiency ofsingle layer organic light emitting elements better (or in order toperform drive at a low voltage), it is necessary to use a materialcapable of transporting both electrons and holes with a good balance(hereafter referred to as a “bipolar material”). Alq₃ does not satisfythis condition.

[0013] However, provided that a single heterostructure like that ofreference 1 is applied, electrons injected from the cathode are blockedby an interface between a hole transporting layer and an electrontransporting and light emitting layer, and are confined within theelectron transporting and light emitting layer. Carrier recombinationtherefore occurs with good efficiency in the electron transporting andlight emitting layer, and light emission having good efficiency isachieved.

[0014] Expanding upon the concept of a blocking function of this type ofcarrier, it becomes easy to control the carrier recombination region.For example, it has been reported that a hole transporting layer hasbeen successfully made to emit light by confining holes within the holetransporting layer through inserting a layer capable of blocking holes(hole blocking layer) between a hole transporting layer and an electrontransporting layer. (reference 2: Kijima, Y., Asai, N., and Tamura, S.,“A Blue Organic Light Emitting Diode”, Japanese Journal of AppliedPhysics. Vol. 38, pp. 5274-5277 (1999)).

[0015] Further, the organic light emitting elements of reference 1perform separation of functions in that hole transportation is performedby the hole transporting layer, and electron transportation and lightemission are performed by the electron transporting and light emittinglayer. The concept of the function separation is further expanded uponto the concept of a double heterostructure (three-layered structure) inwhich a light emitting layer is sandwiched by a hole transporting layerand an electron transporting layer (reference 3: Adachi, C., Tokoto, S.,Tsutsui, T., and Saito, S., “Electroluminescence in Organic Films with aThree-layered Structure”, Japanese Journal of Applied Physics, Vol. 27,No. 2, pp. L269-L271 (1988)).

[0016] An advantage of the so-called separation of functions is that theneed to make one type of organic material possess several types offunctions (such as the ability to emit light. carrier transportingproperties, the ability to inject carriers from electrodes), andtherefore separation of functions provides a wide ranging amount offreedom in molecular design and the like (for example, there is nolonger a need to search unreasonably for a bipolar material). In otherwords, high efficiency light emission can be easily achieved bycombining materials such as a material having good light emittingproperties and a material with superior carrier transporting properties,respectively.

[0017] The lamination structure discussed in reference 1 thereforeenjoys widespread use at present due to these advantages (carrierblocking function and separation of functions).

[0018] However, interface boundaries (hereafter referred to as “organicinterfaces”) develop between each layer with a lamination structure likethat discussed above because the structure is made of junction ofdifferent types of substances. Two problems which have their origin inthe formation of organic interfaces are presented below.

[0019] First, one problem is hindrance of an additional reduction in adriver voltage. It has been reported for organic light emitting elementsthat in practice, single layer structure elements using a conjugatepolymer are superior with regard to the driver voltage, and that topdata power efficiency (units of 1 m/W) is maintained (compared to lightemission from a singlet excitation state). (reference 4: Tsutsui, T., J.Applied Physics Society Organic Molecules—Bio-electronics Section, Vol.11, No. 1, p. 8 (2000). (However, this is compared to light emissionfrom a singlet excitation state, and excludes light emitted from atriplet excitation state.) Note that the conjugate polymers discussed inreference 4 are bipolar materials, and that a level of carrierrecombination efficiency equivalent to that of a lamination structurecan be achieved. In practice, a single layer structure having feworganic interfaces therefore shows a lower driver voltage provided thatthe carrier recombination efficiency can be made equivalent. without theuse of a lamination structure, by a method such as using a bipolarpolymer. This eventually suggests that carrier mobility in the organicinterface is hindered.

[0020] In addition, another problem originates in an organic interfaceis exertion of influence on the element lifetime (element deterioration)for organic light emitting elements. Namely, brightness drops becausethe carrier mobility is impeded and charge accumulates.

[0021] No definite theory has been established regarding the mechanismof this degradation, but it has been reported that the drop inbrightness can be suppressed by inserting a hole injecting layer betweenthe anode and the hole transporting layer, and in addition, byperforming ac drive at a short wavelength instead of dc drive (reference5: VanSlyke, S. A., Chen, C. H., and Tang, C. W., “OrganicElectroluminescent Devices with Improved Stability”, Applied PhysicsLetters, Vol. 69, No. 15, pp. 2160-2162 (1966)). This can be said to beexperimental evidence that the reduction in brightness can be suppressedin accordance with eliminating charge accumulation by inserting the holeinjecting layer and by using ac drive.

[0022] From the above discussion, the lamination structure has themerits of being able to easily increase the carrier recombinationefficiency (carrier blocking function), and being able to increase thebreadth of selection of materials (separation of functions). However,carrier mobility is suppressed due to the formation of organicinterfaces, in particular interfaces which block carriers, and this inturn influences the reductions in the driver voltage and in brightness.

SUMMARY OF THE INVENTION

[0023] An object of the present invention is to eliminate organicinterfaces existing within an organic compound film, thereby increasingcarrier mobility, by manufacturing elements that differ in concept fromlamination structure conventionally used, and at the same time, toexpress function of a plurality of materials (hereafter referred to as“function expression”) similar to the function separation of thelamination structure. In addition, an object of the present invention isto provide organic light emitting elements having a lower driver voltagethan, and a longer element lifetime than, conventional elements usingfunction expression.

[0024] Further, an object of the present invention is to provide a lightemitting device having a lower driver voltage than, and a longerlifetime than, conventional devices by using the organic light emittingelements. In addition, an object of the present invention is to provideelectronic equipment that has a lower electric power consumption than,and a longer lifetime than. conventional electronic equipment bymanufacturing the electronic equipment using the above-mentioned lightemitting device.

[0025] The inventors of the present invention considered the twomechanisms which will be discussed below as models for inhibitingcarrier mobility by forming an organic interface.

[0026] First, one mechanism developing from the morphology of theorganic interface was considered. An organic compound film in an organiclight emitting element is normally an amorphous state film, and isformed by aggregation of molecules of the organic compound in accordancewith forces between molecules, mainly dipolar interactions. However, ifa heterostructure is formed using this type of molecular aggregate, thenthere is the possibility of that the difference in molecular size andshape will have a great influence in the heterostructure interface(namely, the organic interface).

[0027] In particular, the conformity of junction in the organicinterface is thought to become worse for cases in which aheterostructure is formed using materials having large differences intheir molecular size. A conceptual diagram thereof is shown in FIG. 1. Afirst layer 111 made from small molecules 101 and a second layer 112made from large molecules 102 are laminated in FIG. 1. A region 114having poor conformity develops in an organic interface 113 in thiscase.

[0028] There is a possibility that the poor conformity region 114 shownin FIG. 1 will become a barrier (or energy barrier) which inhibitscarrier mobility, and this suggests that it hinders the driver voltagefrom being additionally reduced. Furthermore, carriers unable toovercome the energy barrier accumulate as a charge, and there is apossibility that this will cause a drop in brightness as discussedabove.

[0029] Another mechanism developing from processes of forming thelamination structure (namely, forming the organic interface) was alsoconsidered. Organic light emitting elements are normally manufacturedusing a multi-chamber method (in-line method) evaporation apparatus inorder to avoid contamination when forming each layer of the laminationstructure, as shown in FIG. 2.

[0030] An evaporation apparatus for forming a three layered structure ofa hole transporting layer, a light emitting layer, and an electrontransporting layer (a double heterostructure) is shown in the example ofFIG. 2. First, a substrate having anodes (such as indium tin oxide(hereafter referred to as “ITO”)) is carried into an entrance chamber,and cleaning of the anode surface is performed by irradiatingultraviolet light within a vacuum atmosphere in an ultravioletirradiation chamber. In particular, oxidation processing is performed inthis processing chamber for cases in which the anode is an oxide such asITO. In addition, hole transporting layers are formed in an evaporationchamber 201, light emitting layers (three colors: red, green, and bluein FIG. 2) are formed in evaporation chambers 202 to 204, electrontransporting layers are formed in an evaporation chamber 205 andcathodes are formed in an evaporation chamber 206 in order to form eachlayer of the lamination structure. Sealing is performed lastly in asealing chamber, and the organic light emitting elements are taken outfrom an exit chamber.

[0031] A feature of this type of in-line method evaporation apparatus isthat the evaporation of each layer is performed in different evaporationchambers, namely the evaporation chambers 201 to 205, respectively. Inother words, this is an apparatus structure in which materials for eachlayer do not mix with each other.

[0032] Incidentally, although the inside of the evaporation apparatus isreduced in pressure to normally be on the order of 10⁻⁴ to 10⁻⁵ Pa, avery small amount of gaseous components (such as oxygen and water)remain. Even with this very small amount of gaseous components, anadsorbed layer on the order of a single molecular layer is easily formedin several seconds at this level of vacuum.

[0033] A large interval therefore develops between the formation of eachlayer when manufacturing organic light emitting elements of laminationstructures using an apparatus like that of FIG. 2. In other words, thereis a fear that adsorbed layers (hereafter referred to as “impuritylayers”) will form due to a very small amount of gaseous componentsduring the intervals between the formation of each layer, in particularwhen conveying occurs via a second conveyor chamber.

[0034] A conceptual diagram of such is shown in FIG. 3. FIG. 3 shows astate in which an impurity layer 313 composed of a very small amount ofan impurity 303 (such as water or oxygen) is formed between a firstlayer 311 made from a first organic compound 301, and a second layer 312made from a second organic compound 302, during lamination of the twolayers.

[0035] The impurity layer thus formed between each of the layers(namely, an organic interface) becomes an impurity region that trapscarriers, thereby inhibiting the mobility of the carriers, aftercompletion of the organic light emitting elements, and therefore thedriver voltage is increased. In addition, charge will accumulate in thecarrier trapping an impurity region if it exists, and therefore there isa possibility of inducing a reduction in brightness like that discussedabove.

[0036] Considering this type of mechanism, it is necessary to go beyondconventional lamination structure elements for both the elementstructure and the manufacturing processes in order to overcome theproblems which develop in the organic interface (deterioration of themorphology of the organic interface and formation of an impurity layer)discussed above. For example, organic light emitting elements havingonly a single layer, in which a hole transporting material is mixed withan electron transporting material (hereafter referred to as a “mixedsingle layer”), formed between two electrodes have been reported asexamples of organic light emitting elements which completely eliminateorganic interfaces (reference 6: Naka, S., Shinno, K. l, Okada, H.,Onnagawa, H., and Miyashita, K., “Organic Electroluminescent DevicesUsing a Mixed Single Layer”, Japanese Journal of Applied Physics, Vol.33, No. 12B, pp. L1772-L1774 (1994)).

[0037] A single layer structure is formed in reference 6 by mixing4,4′-bis[N-(3-methylphenyl)-N-phenyl-amino]-biphenyl (hereafter referredto as “TPD”) with Alg₃, which have hole transporting properties andelectron transporting properties, respectively, in a ratio of 1:4.However, it is shown that the single layer structure is inferiorcompared to a lamination structure (namely, a heterostructure made fromTPD and Alq₃ and in which an organic interface is formed) from the pointof light emission efficiency. Although the efficiency of light emissioncan be greatly improved by doping a light emitting material, there isstill a certain amount of inferiority compared to a lamination structuredoped with a light emitting material.

[0038] The cause for this is thought to be that holes injected from theanode and electrons injected from the cathode tend to pass through tothe opposite electrode without recombining in the mixed single layercase. The lamination structure has a carrier blocking function, andtherefore this type of problem does not develop.

[0039] In other words, this is because function expression is notperformed in the mixed single layer of reference 6. That is, if regionscapable of expressing each of the functions are not formed. for examplea region near the anode exhibits a hole transporting function, a regionnear the cathode exhibits an electron transporting function within theorganic compound film, and light emitting regions (regions in which thecarriers recombine) are formed in portions separated from both theelectrodes, then light emission with good efficiency cannot be achievedeven if the organic interfaces are eliminated.

[0040] In consideration of these points, the inventors of the presentinvention proposed a method for achieving organic light emittingelements that differ from those of reference 6 but which are capable offunction expression and in which organic interfaces are eliminated. Aconceptual diagram of such is shown in FIG. 4. Note that, although ananode 402 is formed on a substrate 401 here, a reversed structure inwhich a cathode 404 is formed on the substrate may also be used.

[0041] A hole transporting region 405 made from a hole transportingmaterial 430, an electron transporting region 409 made from an electrontransporting material 431, and a mixture region 407 in which the holetransporting material and the electron transporting material are mixedat a fixed ratio (hereafter referred to as “x:y”) are formed in anorganic compound film 403 containing the hole transporting material andthe electron transporting material for elements shown in FIG. 4. A lightemitting region 432 is formed in the mixture region 407 by adding alight emitting material 410 which emits light.

[0042] In addition, a first concentration change region 406 and a secondconcentration change region 408 are formed between the mixture region407 and the hole transporting region 405, and between the mixture region407 and the electron transporting region 409, respectively. Aconcentration gradient is formed in the concentration change regions sothat the concentration ratio gradually becomes closer to the x:y ratioof the mixture region. A schematic diagram of the concentration profileis shown in FIG. 5.

[0043] The hole transporting material can receive and transport holes atthe anode side, and on the other hand the electron transporting materialcan receive and transport electrons at the cathode side when this typeof element is formed. Further, a gentle concentration gradient is formedin the concentration change regions 406 and 408 so as to avoid a suddenconcentration change (the most extreme example of a sudden change is aconventional heterostructure, in which the concentration changes from 0%to 100%, or from 100% to 0%), and therefore the energy barrier withrespect to the carriers can be nearly eliminated.

[0044] The carrier input to the organic compound film 403 is thereforetransported smoothly to the mixture region 407 without being obstructedby a large energy barrier. This is a very important role that theconcentration change regions 406 and 408 play. In addition, the mixtureregion 407 has bipolarity, and therefore it becomes possible for boththe holes and electrons to move in the mixture region 407.

[0045] What is important here is that the light emitting regioncontaining the light emitting material is formed in the mixture region407. In other words, carriers can be prevented from passing through themixture region without recombining, and at the same time the lightemitting region is kept away from the electrodes and disruption of lightby the electrodes (hereafter referred to as “quenching”) can beprevented, by adding the light emitting material 410 to the mixtureregion 407. Regions in which each function (carrier transport and lightemission) can be expressed thus exist within the organic compound film403, differing from the mixed single layer of reference 6.

[0046] In addition, organic interfaces like those of conventionallamination structures do not exist within this type of element. Theaforementioned problems that develop at the above-mentioned organicinterface (morphology deterioration of the organic interface andformation of an impurity layer) can therefore be solved.

[0047] First, an explanation of how the morphology deterioration of theorganic interface is resolved is made using FIG. 6. FIG. 6 is a crosssection of an organic compound film made from a region 611 composed ofsmall molecules 601, a region 612 composed of large molecules 602, and amixture region 613 containing both the small molecules 601 and the largemolecules 602. Note that a concentration change region has been omittedhere for convenience in the figure. FIG. 6 makes clear that an organicinterface like the organic interface 113 of FIG. 1 does not exist here.and that the region 114 having poor conformity does not exist either.

[0048] Further, formation of an impurity layer is resolved. Whenmanufacturing organic light emitting elements like those of FIG. 4, thehole transporting material is initially formed on the anode byevaporation, then, during the evaporation of the hole transportingmaterial, an electron transporting material is stated to beco-evaporated in addition to the hole transporting material whereby themixture region is formed, and then, the evaporation of the holetransporting material is stopped while the evaporation of the electrontransporting material is continued. An interval that arises duringmanufacturing of organic light emitting elements when using anevaporation apparatus like that of FIG. 2 therefore does not exist.Namely, no opportunity is provided for the formation of an impuritylayer.

[0049] Organic interfaces are thus not formed in the organic lightemitting elements of the present invention, and therefore carriermobility is smooth and no adverse influence is exerted on the drivervoltage or the element lifetime. In addition, there is functionseparation similar to that of a lamination structure, and thus there areno problems relating to efficiency of light emission.

[0050] Furthermore, the structure of the present invention has amixed-junction and not the hetero-junction between different substanceswith a conventional lamination structure, and the light emittingelements of the present invention are based upon a novel concept.

[0051] Therefore, with the present invention, a light emitting device isformed having an organic light emitting element, the organic lightelement having:

[0052] an anode;

[0053] a cathode; and

[0054] an organic compound film containing a hole transporting materialand an electron transporting material;

[0055] wherein:

[0056] the organic compound film has a structure in which:

[0057] a hole transporting region made from the hole transportingmaterial;

[0058] a first concentration change region in which the proportion ofthe electron transporting material increases gradually until a ratiobetween the hole transporting material and the electron transportingmaterial becomes x:y (where x and y are positive constants);

[0059] a mixture region containing the hole transporting material andthe electron transporting material at the ratio of x:y;

[0060] a second concentration change region in which the proportion ofthe electron transporting material gradually increases further from thex:y ratio; and

[0061] an electron transporting region made from the electrontransporting material;

[0062] exist in order in a direction from the anode to the cathode; and

[0063] a light emitting region, into which a light emitting material forperforming light emission is added, is formed within the mixture region.

[0064] Note that it is preferable that the energy difference between ahighest occupied molecular orbital (HOMO) and a lowest unoccupiedmolecular orbital (LUMO) of the light emitting material (hereafterreferred to as “excitation energy level”) be smaller compared to that ofthe hole transporting material and electron transporting material. Thisis in order to prevent energy mobility of molecular excitons of thelight emitting material.

[0065] Further, a hole injecting region made from a material forenhancing injecting properties of holes (hereafter referred to as a“hole injecting material”) may also be inserted between the anode andthe organic compound film in FIG. 4. Furthermore, an electron injectingregion made from a material for enhancing injecting properties ofelectrons (hereafter referred to as an “electron injecting material”)may also be inserted between the cathode and the organic compound film.Both the hole injecting region and the electron injecting region mayalso be included.

[0066] The hole injecting material and the electron injecting materialin this case are materials for reducing the carrier injecting barrierfrom the electrodes to the organic compound film, and therefore carriermobility from the electrodes to the organic compound film is smooth. Thematerials have an effect of being capable of eliminating chargeaccumulation. However, from the viewpoint of avoiding formation of animpurity layer like that discussed above, it is preferable that nointerval occurs in formation of the films between each of the injectingmaterials and the organic compound film.

[0067] Further, a carrier recombination portion is nearly determined bythe mixture ratio in the mixture region (becoming closer to the centerthe more bipolar the ratio becomes). The light emitting material maytherefore be added to the entire region within the mixture region (seeFIG. 7A), and may be added to only a portion of the mixture region (seeFIG. 7B).

[0068] In addition, a structure in which a blocking material 411 may beadded to the mixture region 407, as shown in FIG. 8A. Note that althoughthe anode 402 is formed on the substrate 401 here, an inverse structurein which the cathode 404 is formed on the substrate may also be used.Furthermore, the hole injecting region and the electron injecting regionmay also be formed between the electrodes and the organic compound film.

[0069] Note that the term blocking material denotes a material havingthe highest excitation energy among the materials contained in themixture region 407 and which functions so as to block carriers. Inaddition, it functions so as to prevent the diffusion of molecularexcitons. The carrier recombination rate in the mixture region 407increases, and diffusion of molecular excitons is prevented if theblocking material 411 is added to the mixture region 407, and thereforea high light emission efficiency can be expected. However, blockingmaterials often have a blocking function for only holes or electrons,and therefore the carrier balance within the mixture region may breakdown if the blocking material is added throughout the entire mixtureregion. Accordingly, it is more preferable that the blocking material isadded only to a portion of the mixture region.

[0070] Further, materials having a low HOMO level, namely those capableof blocking holes, are normally effective for the blocking material. Thetechnique of adding the blocking material 411 to a place closer to thecathode side than the region in which the light emitting material 410 isadded, as shown in FIG. 8B, is therefore effective.

[0071] In recent years, from the viewpoint of the light emittingefficiency, organic light emitting elements capable of transformingenergy emitted when returning from a triplet excitation state to a basestate (hereafter referred to as “triplet excitation energy”) have beenin the spotlight due to their high light emission efficiency (reference7: O'Brien, D. F., Baldo, M. A., Thompson, M. E., and Forrest, S. R.,“Improved Energy Transfer in Electrophosphorescent Devices”, AppliedPhysics Letters, Vol. 74, No. 3, pp. 442-444 (1999); and reference 8:Tsutsui, T., Yang, M. J., Yahiro, M., Nakamura, K., Watanabe, T., Tsuji,T., Fukuda, Y., Wakimoto, T., and Miyaguchi, S, “High Quantum Efficiencyin Organic Light-Emitting Devices with Iridium-Complex as a TripletEmissive Center”, Japanese Journal of Applied Physics, Vol. 38, pp.L1502-L1504 (1999)).

[0072] A metal complex in which platinum is a central metal, and a metalcomplex in which iridium is a central metal, are used in reference 7 andreference 8, respectively. Organic light emitting elements capable ofconverting these triplet excitation energy into light emission(hereafter referred to as “triplet light emitting elements”) can achievehigher light emitting brightness, and high light emitting efficiency,than conventional light emitting elements.

[0073] However, the half-value period for the brightness for a case inwhich the initial brightness is set to 500 cd/m² is on the order of 170hours in accordance with the example reported in reference 8, and thisis a problem for the lifetime of the elements. A light emitting layerusing a suitable host material with respect to a light emitting materialand a blocking layer using a single blocking material for preventing thediffusion of molecular excitons are necessary for the triplet lightemitting elements, and therefore becomes a lamination structure and anumber of organic interfaces develop is thought to be a cause of theshort element life.

[0074] Light emitting elements having extremely high function in whichhigh brightness light emission and high light emitting efficiency inaccordance with light emission from a triplet excitation state, and along element lifetime, become possible by applying the present inventionto triplet state light emitting elements. Note that triplet molecularexcitons have a dispersion distance which is large in comparison withsinglet molecular excitons, and therefore it is preferable that ablocking material be contained in a mixture region.

[0075] Incidentally, bipolarity is necessary for the mixture region, andtherefore it is preferable to set the mass percentage of a holetransporting material to be greater than or equal to 10%, and less thanor equal to 90%, with respect to the total mass of the hole transportingmaterial and an electron transporting material. Note that this ratio isthought to vary considerably in accordance with the combination of thematerial .

[0076] Further, the mixture region contains a light emitting region inthe present invention, namely a region in which carriers recombine, andtherefore a thickness on an order such that carriers do not pass throughis necessary. It is therefore preferable that the mixture region have athickness equal to or greater than 10 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] In the accompanying drawings:

[0078]FIG. 1 is a diagram for expressing an organic interface state;

[0079]FIG. 2 is a diagram showing an evaporation apparatus;

[0080]FIG. 3 is a diagram showing formation of an impurity layer;

[0081]FIG. 4 is a diagram showing a structure of an organic lightemitting element;

[0082]FIG. 5 is a diagram showing a concentration profile;

[0083]FIG. 6 is a diagram for expressing a mixture region state;

[0084]FIGS. 7A and 7B are diagrams showing structures of an organiclight emitting element;

[0085]FIGS. 8A and 8B are diagrams showing structures of an organiclight emitting element;

[0086]FIGS. 9A and 9B are diagrams showing an evaporation apparatus:

[0087]FIG. 10 is a diagram showing a structure of an organic lightemitting element;

[0088]FIGS. 11A and 11B are diagrams showing cross sectional structuresof a light emitting device;

[0089]FIG. 12 is a diagram showing a cross sectional structure of alight emitting device;

[0090]FIGS. 13A and 13B are diagrams showing an upper surface structureand a cross sectional structure, respectively, of a light emittingdevice;

[0091]FIG. 14 is a diagram showing a cross sectional structure of alight emitting device;

[0092]FIGS. 15A to 15C are diagrams showing an upper surface structure.and cross sectional structures, respectively, of a light emittingdevice;

[0093]FIG. 16A and 16B are diagrams showing structures of a lightemitting device;

[0094]FIGS. 17A and 17B are diagrams showing structures of a lightemitting device;

[0095]FIGS. 18A to 18C are diagrams showing structures of a lightemitting device;

[0096]FIGS. 19A to 19F are diagrams showing specific examples ofelectronic equipment;

[0097]FIGS. 20A and 20B are diagrams showing specific examples ofelectronic equipment; and

[0098]FIG. 21 is a diagram showing a structure of a light emittingdevice.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode

[0099] An embodiment when implementing the present invention isdiscussed below. Note that at least one of an anode and a cathode mustbe transparent in order to extract light emission from an organic lightemitting element. An element structure in which a transparent anode isformed on a substrate and light is extracted from the anode is discussedhere. In practice, it is also possible to apply the present invention toa structure in which light is extracted form the cathode and to astructure in which light is extracted from the side opposite to that ofthe substrate.

[0100] Production processes for manufacturing organic light emittingelements become very important in order to prevent the formation ofimpurity layers when implementing the present invention. A method ofmanufacturing an organic light emitting element disclosed by the presentinvention is discussed first.

[0101]FIG. 9A is an upper surface diagram of an evaporation apparatus,and one vacuum chamber 910 is set up as an evaporation chamber 943, anda plurality of evaporation sources 944 are formed within the vacuumchamber, resulting in a single chamber method. Materials havingdifferent functions, such as a hole injecting material, a holetransporting material, an electron transporting material, an electroninjecting material, a blocking material a light emitting material, and acathode structuring material are stored separately in the respectiveplurality of evaporation sources.

[0102] A substrate having an anode (such as ITO) first goes into anentrance chamber 940 in this type of evaporation apparatus having anevaporation chamber, and oxidation processing is performed in apreprocessing chamber 941 if the anode is an oxide such as ITO (notethat, although not shown in FIG. 9A, it is also possible to establish anultraviolet irradiation chamber for cleaning the surface of the anode).In addition, all materials for forming the organic light emittingelements are evaporated within the vacuum chamber 910. However, thecathode may be formed within the vacuum chamber 910, and the cathode mayalso be formed in a separate evaporation chamber. The point is that aperiod up through forming the cathode may take place by evaporationwithin one vacuum chamber, the vacuum chamber 910. Sealing is performedlastly in a sealing chamber 942, the substrate is removed from an exitchamber, and the organic light emitting elements are thereby obtained.Note, 945 denotes a conveyor chamber.

[0103] Processes for manufacturing the organic light emitting elementsof the present invention using this type of single chamber method areexplained using FIG. 9B (a cross sectional diagram of the vacuum chamber910). A process of forming an organic compound film containing a holetransporting material 921, an electron transporting material 922, and alight emitting material 923 using the vacuum chamber 910 having threeevaporation sources (an organic compound evaporation source a 916, anorganic compound evaporation source b 917, and an organic compoundevaporation source c 918) is shown in FIG. 9B as the simplest example.

[0104] First, a substrate 901 having an anode 902 enters the inside ofthe vacuum chamber 910, and is fixed to a fixture plate 911 (thesubstrate is normally rotated during evaporation). Next, the inside ofthe vacuum chamber 910 is reduced in pressure (preferably to 10⁻⁴ Pa orless), after which a container a 912 is heated, making the holetransporting material 921 evaporate, and a shutter a 914 is opened whena predetermined evaporation rate (units of Å/s) is achieved. Evaporationthus begins. A shutter b 915 remains closed at this point, and acontainer b 913 is also heated.

[0105] A shutter b 915 is gradually opened when a predeterminedthickness of a hole transporting region 903 is achieved, and theevaporation rate of the electron transporting material 922 is increased.The shutter a 914 may remain open as is, and it may also be graduallyclosed, reducing the evaporation rate of the hole transporting material.A concentration gradient in a first concentration change region 904 isformed in accordance with the speeds for opening and closing theshutters at this time.

[0106] Next, shutter opening and closing operations are stopped at apoint when a predetermined ratio x:y is achieved for the proportion ofthe hole transporting material 921 to the electron transporting material922, and a mixture region 905 is formed at a constant evaporation rate.A very small amount of the light emitting material 923 may also be addedhere when forming the mixture region 905 (state shown in FIG. 9B).

[0107] The shutter a 914 is gradually closed when a predeterminedthickness is reached for the mixture region 905, and the evaporationrate of the hole transporting material 921 is reduced. The shutter b 915may be left as is, and it may also be gradually opened, therebyincreasing the evaporation rate of the electron transporting material922. A concentration gradient in a second concentration change region isformed in accordance with the speeds for opening and closing theshutters. In addition, the shutter a 914 is completely closed in orderto form an electron transporting region, and heating of the container a912 is stopped.

[0108] The aforementioned operations are all performed without causingany intervals to occur, and therefore impurity layers are not mixed intoany of the regions.

[0109] It is possible to manufacture all of the organic light emittingelements discussed as means for resolving the objects of the presentinvention by applying this method. For example, an evaporation sourcefor evaporating a blocking material may be established in FIG. 9B forcases in which the blocking material is added to the mixture region 905,and the blocking material may be evaporated during formation of themixture region.

[0110] Further, for cases in which a hole injecting region and anelectron injecting region are formed, evaporation sources for eachinjecting material may be set within the same vacuum chamber, the vacuumchamber 910. For example, if a hole injecting region is formed byevaporation between the anode 902 and the hole transporting region 903in FIG. 9B, then formation of an impurity layer can be averted byevaporating the hole transporting material 921 immediately afterevaporating a hole injecting material on the anode 902, without aninterval.

[0111] Next, examples are given below of preferred materials formaterials such as hole injecting materials, hole transporting materials,electron transporting materials, electron injecting materials. blockingmaterials, and light emitting materials. Note that materials capable ofbeing used in the organic light emitting elements of the presentinvention are not limited to the materials discussed below.

[0112] Porphyrin compounds are effective as hole injecting materials ifan organic compound is used, such as phthalocyanine (hereafter referredto as “H2Pc”) and copper phthalocyanine (hereafter referred to as“CuPc”). There are also materials in which chemical doping is performedto a conductive polymer compound, and materials such as polyethylenedioxythiofuran (hereafter referred to as “PEDOT”) doped with polystyrenesulphonic acid (hereafter referred to as “PSS”), and polyaniline.Further, polymer compound insulators are also effective in leveling, andpolyimide (hereafter referred to as “PI”) is often used. In addition,inorganic compounds are also used, such as metallic thin films of goldor platinum, and ultra thin films of aluminum oxide (hereafter referredto as “alumina”).

[0113] Aromatic amine compounds (namely, compounds having bonds betweena benzene ring and nitrogen) are the most widely used as holetransporting materials. In addition to TPD discussed above, derivativesof TPD such as the starburst aromatic amine compounds4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereafter referred toas “α-NPD”), 4,4′,4″-tris(N,N-di phenyl-amino)-triphenylamine (hereafterreferred to as “TDATA”), and 4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenylamine (hereafter referred to as“MTDATA”) can be given as the widely used materials.

[0114] Metal complexes are often used as electron transportingmaterials, and metal complexes having quinoline skeletons or benzoquinoline skeletons, such as Alq₃, discussed above,tris(4-methyl-8-quinolinolate) aluminum (hereafter referred to as“Almq₃”), and bis(10-hydroxybenzo[h]quinolinate) beryllium (hereafterreferred to as “BeBq₂”) exist, as do materials such as the mixed ligandcomplex bis(2-methyl-8-quinolinolate)-(4-hydroxy-biphenyl)-aluminum(hereafter referred to as “BAlq”). Further, there are also metalcomplexes having oxazoles or thiazolate ligands, such asbis[2-(2-hydroxyphenyl)-benzooxazolate] zinc (hereafter referred to as“Zn(BOX)₂”), bis[2-(2-hydroxyphenyl)-benzothiazolate] zinc (hereafterreferred to as “Zn(BTZ)₂”). In addition to metal complexes, oxadiazolederivatives such as2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (hereafterreferred to as “PBD”) and1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-il] benzene (hereafterreferred to as “OXD-7”) also have electron transporting properties.Triazole derivatives such as3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenyl)-1,2,4-triazole (hereafterreferred to as “TAZ”) and3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenilyl-1,2,4-triazole(hereafter referred to as “p-EtTAZ”), and phenanthroline derivativessuch as vasophenanthrene (hereafter referred to as “BPhen”) andvasocuproin (hereafter referred to as “BCP”) also have electrontransporting properties.

[0115] The electron transporting materials stated above can be used aselectron injecting materials. In addition, ultra thin films ofinsulators of alkaline metal halogen compounds such as lithium fluoride,and alkaline metallic oxide such as lithium oxide are also often used.Furthermore, alkaline metal complexes such as lithium acetylacetate(hereafter referred to as “Li(acac)”) and 8-quinolinolate-lithium(hereafter referred to as “Liq”) are also effective.

[0116] The aforementioned materials BAlq, OXD-7, TAZ, p-EtTAZ, BPhen,BCP, and the like are effective as blocking materials due to their highexcitation energy level.

[0117] In addition to metal complexes such as the aforementioned Alq₃,Almq₃, BeBq₂, BAlq, Zn(BOX)₂, and Zn(BTZ)₂, various types of fluorescentpigments are also effective as light emitting materials. Further, it isalso possible to use triplet light emitting materials as tight emittingmaterials, and complexes having platinum or iridium as a central metalare mainly used. Materials such as tris(2-phenylpyridine) iridium(hereafter referred to as “Ir(ppy)₃”) and 2,3,7,8,12,13,17,18-octaethyl-21 H,23H-porphyrin-platinum (hereafter referred to as“PtOEP”) are known as triplet light emitting materials.

[0118] Organic light emitting elements having a lower driver voltage,and a longer element lifetime, than conventional light emitting elementscan be manufactured by combining the materials having differentfunctions that are discussed above and applying them to the organiclight emitting elements of the present invention.

Embodiments Embodiment 1

[0119] A specific example of an organic light emitting element in whicha hole injecting region made from a hole injecting material is insertedbetween the anode 402 and the organic compound film 403 is shown in thisembodiment for the organic light emitting elements of FIG. 7A.

[0120] First, the glass substrate 401 on which a film is formed from ITOby sputtering to a thickness on the order of 100 nm and the anode 402 isformed is prepared. The glass substrate 401 having the anode 402 is thenconveyed to the inside of a vacuum chamber like that shown in FIGS. 9Aand 9B. Five evaporation sources are necessary in this embodiment inorder to evaporate five types of materials (four of the materials areorganic compounds, and one is a metal that becomes a cathode).

[0121] The hole injecting material CuPc is evaporated for 20 nm first,and when the 20 nm thickness of CuPc evaporation is completed,evaporation of the hole transporting material α-NPD at an evaporationrate of 3 Å/sec is started without creating an interval. The reason thatan interval is not formed is in order to prevent the formation of animpurity layer, as discussed above.

[0122] After forming the hole transporting region 405 composed of onlyα-NPD with a thickness of 20 nm, the shutter to the electrontransporting material Alq₃ evaporation source is gradually opened whilethe evaporation rate of α-NPD remains fixed at 3 Å/sec. The firstconcentration change region 406 having a concentration gradient is thusformed having a thickness on the order of 10 nm. The evaporation rate ofAlq₃ is regulated so as to become 3 Å/sec when a thickness of 10 nm isreached for the first concentration change region 406.

[0123] Next, the evaporation rate of Alq₃ is fixed at 3 Å/sec so thatthe evaporation rate ratio between α-NPD and Alq₃ becomes 1:1, and themixture region 407 is formed by co-evaporation. The fluorescent pigmentN,N′-dimethyl quinacridon (hereafter referred to as “MQd”) is added atthe same time as the light emitting material 410. The evaporation rateof MQd is controlled so that the proportion of MQd becomes on the orderof 1 wt % of the total.

[0124] Evaporation of MQd is stopped after the mixture region 407reaches a thickness of 30 nm, and the shutter to the α-NPD evaporationsource is gradually closed with the evaporation rate of Alq₃ fixed at 3Å/sec. The second concentration change region 408 having a concentrationgradient is thus formed having a thickness on the order of 10 nm.Evaporation of α-NPD is stopped when the second concentration changeregion 408 has reached a thickness of 10 nm.

[0125] In addition, the electron transporting region 409 can be formedby continuing to evaporate only Alq₃. Its thickness is set to 40 nm.Lastly, an organic light emitting element that emits green color lightoriginated from MQd is obtained by evaporating an Al:Li alloy to athickness on the order of 150 nm as the cathode.

Embodiment 2

[0126] A specific example of the organic light emitting element shown inFIG. 8B is shown in this embodiment.

[0127] First, the glass substrate 401 on which a film is formed from ITOby sputtering to a thickness on the order of 100 nm and the anode 402 isformed is prepared. The glass substrate 401 having the anode 402 is thenconveyed to the inside of a vacuum chamber like that shown in FIGS. 9Aand 9B. Five evaporation sources are necessary in this embodiment inorder to evaporate five types of materials (four of the materials areorganic compounds, and one is a metal that becomes a cathode).

[0128] After forming the hole transporting region 405 to a thickness of30 nm only from the hole transporting material MTDATA (evaporation rateof 3 Å/sec), the shutter to the MTDATA evaporation source is graduallyclosed, while the shutter to an evaporation source of the electrontransporting material PBD is gradually opened. The first concentrationchange region 406 with a thickness on the order of 10 nm having aconcentration gradient is thus formed. The evaporation rate of MTDATA isregulated so as to be 1 Å/sec, and the evaporation rate of PBD isregulated so as to be 4 Å/sec, once the first concentration changeregion 406 has reached a thickness of 10 nm.

[0129] Next, with the evaporation rates of MTDATA and PBD fixed at 1Å/sec and 4 Å/sec, respectively, so as to form an evaporation rate ratioof 1:4 for MTDATA and PBD, the mixture region 407 is formed with athickness of 30 nm by co-evaporation. The fluorescent pigment peryleneis added as the light emitting material 410 to the intermediate 10 nm ofthe mixture region 407 (namely, between the 10 and 20 nm levels of the30 nm thick mixture region). The addition of perylene is implementedsuch that the ratio of perylene to the entire weight is on the order of5 wt %. Further, BCP is added as the blocking material 411 to the final10 nm of the mixture region 407 (namely, between the 20 and 30 nm levelsof the 30 nm thick mixture region). The addition of BCP is performedsuch that the evaporation rate ratio becomes MTDATA:PBD:BCP=1:4:5 (inother words, BCP is evaporated at a rate of 5 Å/sec).

[0130] Evaporation of BCP is stopped after the mixture region 407reaches a thickness of 30 nm, and the shutter of the MTDATA evaporationsource is gradually closed while the evaporation rate of PBD is fixed at4 Å/sec. The second concentration change region 408 having aconcentration gradient is thus formed with a thickness on the order of10 nm. Evaporation of MTDATA is regulated so as to be complete when thesecond concentration change region 408 reaches 10 nm.

[0131] In addition, the electron transporting region 409 is formed bycontinuing to evaporate only PBD. The thickness is made to be 30 nm.Lastly, an organic light emitting element that emits blue color lightoriginated from perylene is obtained by evaporating an Al:Li alloy asthe cathode to a thickness on the order of 150 nm.

Embodiment 3

[0132] A specific example in which a hole injecting region made from ahole injecting material is inserted between the anode 402 and theorganic compound film 403, an electron injecting region made from anelectron injecting material is respectively inserted between the cathode404 and the organic compound film 403, and a triplet light emittingmaterial is applied as the light emitting material in the organic lightemitting element is discussed in this embodiment. The element structureis shown in FIG. 10.

[0133] First, the glass substrate 1000 on which a film is formed fromITO by sputtering to a thickness on the order of 100 nm and the an ITOis formed is prepared. The glass substrate having the ITO is thenconveyed to the inside of a vacuum chamber like that shown in FIGS. 9Aand 9B. Seven evaporation sources are necessary in this embodiment inorder to evaporate seven types of materials (five of the materials areorganic compounds, and two are inorganic compounds that becomecathodes).

[0134] The hole injecting material CuPc is evaporated for 20 nm first,and when a 20 nm thickness of CuPc evaporation is completed, evaporationof the hole transporting material α-NPD at an evaporation rate of 3Å/sec is started without creating an interval. The reason that aninterval is not formed is in order to prevent the formation of animpurity layer, as discussed above.

[0135] After forming the hole transporting region composed of only α-NPDwith a thickness of 20 nm, the shutter of the electron transportingmaterial BAlq evaporation source is gradually opened while theevaporation rate of α-NPD remains fixed at 3 Å/sec. The firstconcentration change region 1001 having a concentration gradient is thusformed having a thickness on the order of 10 nm. The evaporation rate ofBAlq is regulated so as to become 3 Å/sec when a thickness of 10 nm isreached for the first concentration change region.

[0136] Next, with the evaporation rate of BAlq fixed at 3 Å/sec, themixture region 1002 is formed with a thickness of 20 nm byco-evaporating α-NPD and BAlq such that their evaporation rate ratiobecomes 1:1. The triplet light emitting material PtOEP is added as thelight emitting material to the intermediate 10 nm of the mixture region(namely, between the 5 and 15 nm levels of the 20 nm mixture region).The proportion is set such that PtOEP becomes on the order of 6 wt % ofthe total weight.

[0137] The shutter of the evaporation source of α-NPD is graduallyclosed after the mixture region reaches a thickness of 20 nm, while theevaporation rate of BAlq remains fixed at 3 Å/sec. The secondconcentration change region 1003 with a thickness on the order of 10 nmhaving a concentration gradient is thus formed. Evaporation of α-NPD isregulated so as to stop when the second concentration change regionreaches a thickness of 10 nm.

[0138] In addition, the electron transporting region is formed bycontinuing to evaporate only BAlq. Its thickness is set to 10 nm.Evaporation of the electron injecting material Alq₃ is started at thesame time as evaporation of BAlq is complete, without forming aninterval, and a thickness on the order of 30 nm is evaporated. Thereason that an interval is not formed is in order to prevent theformation of an impurity layer, as discussed above.

[0139] The cathode is formed lastly by evaporating LiF to a thickness onthe order of 1 nm, and aluminum to a thickness on the order of 150 nm,and a triplet light emitting element that emits red color lightoriginated from PtOEP is thus obtained.

Embodiment 4

[0140] This embodiment describes a light emitting device that includesan organic light emitting element according to the present invention.FIG. 11 is sectional view of an active matrix light emitting device thatuses an organic light emitting element of the present invention.

[0141] A thin film transistor (hereinafter referred to as TFT) is usedhere as an active element, but the active element may be a MOStransistor. The TFT shown as an example is a top gate TFT (planar TFT,to be specific), but a bottom gate TFT (typically a reverse stagger TFT)may be used instead.

[0142] In FIG. 11A, 1101 denotes a substrate. The substrate used herecan transmit visible light. Specifically, a glass substrate, a quartzsubstrate, a crystal glass substrate, or a plastic substrate (includinga plastic film) can be used. The substrate 1101 refers to the substrateplus an insulating film formed on the surface of the substrate.

[0143] On the substrate 1101, a pixel portion 1111 and a driver circuit1112 are provided. The pixel portion 1111 will be described first.

[0144] The pixel portion 1111 is a region for displaying an image. Aplurality of pixels are placed on the substrate, and each pixel isprovided with a TFT 1102 for controlling a current flowing in theorganic light emitting element (hereinafter referred to as currentcontrolling TFT) 1102, a pixel electrode (anode) 1103, an organiccompound layer 1104. and a cathode 1105. Although only the currentcontrolling TFT is shown in FIG. 11a, each pixel has a TFT forcontrolling a voltage applied to a gate of the current controlling TFT(hereinafter referred to as switching TFT).

[0145] The current controlling TFT 1102 here is preferably a p-channelTFT. Though an n-channel TFT may be used instead, a p-channel TFT as thecurrent controlling TFT is more advantageous in reducing currentconsumption if the current controlling TFT is connected to the anode ofthe organic light emitting element as shown in FIG. 11. Note that, theswitching TFT may be formed by either an n-channel TFT or a p-channelTFT.

[0146] A drain of the current controlling TFT 1102 is electricallyconnected to the pixel electrode 1103. In this embodiment, a conductivematerial having a work function of 4.5 to 5.5 eV is used as the materialof the pixel electrode 1103, and therefore the pixel electrode 1103functions as the anode of the organic light emitting element. Alight-transmissive material, typically, indium oxide, tin oxide, zincoxide, or a compound of these (ITO, for example), is used for the pixelelectrode 1103. On the pixel electrode 1103, the organic compound layer1104 is formed.

[0147] On the organic compound film 1104, the cathode 1105 is provided.The material of the cathode 1105 is desirably a conductive materialhaving a work function of 2.5 to 3.5 eV. Typically, the cathode 1105 isformed from a conductive film containing an alkaline metal element or analkaline-earth metal element, or from a conductive film containingaluminum, or from a laminate obtained by layering an aluminum or silverfilm on one of the above conductive films.

[0148] A layer composed of the pixel electrode 1103, the organiccompound film 1104, and the cathode 1105 is covered with a protectivefilm 1106. The protective film 1106 is provided to protect the organiclight emitting element from oxygen and moisture. Materials usable forthe protective film 1106 include silicon nitride, silicon oxynitride,aluminum oxide, tantalum oxide, and carbon (specifically, diamond-likecarbon).

[0149] Next, the driver circuit 1112 will be described. The drivercircuit 1112 includes a region for controlling timing of signals (gatesignals and data signals) to be sent to the pixel portion 1111, and mayinclude a shift register, a buffer, and a latch, as well as an analogswitch (transfer gate) or level shifter. In FIG. 11A, the basic unit ofthese circuits is a CMOS circuit composed of an n-channel TFT 1107 and ap-channel TFT 1108.

[0150] Known circuit structures can be applied to the shift register,the buffer, the latch, and the analog switch (transfer gate) or levelshifter. Although the pixel portion 1111 and the driver circuit 1112 areprovided on the same substrate in FIG. 11A, IC or LSI may beelectrically connected to the substrate instead of placing the drivercircuit 1112 on the substrate.

[0151] The pixel electrode (anode) 1103 is electrically connected to thecurrent controlling TFT 1102 in FIG. 11A but the cathode may beconnected to the current controlling TFT instead. In this case, thepixel electrode is formed from the material of the cathode 1105 whereasthe cathode is formed from the material of the pixel electrode (anode)1103. The current controlling TFT in this case is preferably ann-channel TFT.

[0152] The light emitting device shown in FIG. 11A is manufactured by aprocess in which formation of the pixel electrode 1103 precedesformation of a wiring line 1109. However, this process could roughen thesurface of the pixel electrode 1103. The roughened surface of the pixelelectrode 1103 may degrade characteristic of the organic light emittingelement since it is a current-driven type element.

[0153] As a modification of FIG. 11A, the pixel electrode 1103 is formedafter forming the wiring line 1109 to obtain a light emitting deviceshown in FIG. 11B. In this case, injection of current from the pixelelectrode 1103 can be improved compared to the structure of FIG. 11A.

[0154] In FIGS. 11A and 11B, a forward-tapered bank structure 1110separates the pixels placed in the pixel portions 1111 from one another.If this bank structure is reverse-tapered, a contact between the bankstructure and the pixel electrode can be avoided. An example thereof isshown in FIG. 12.

[0155] In FIG. 12, a wiring line also serves as a separation portion,forming a wiring line and separation portion 1210. The shape of thewiring line and separation portion 1210 shown in FIG. 12 (namely, astructure with eaves) is obtained by layering a metal that constitutesthe wiring line and a material lower in etch rate than the metal (ametal nitride, for example) and then etching the laminate. This shapecan prevent short circuit between a cathode 1205 and a pixel electrode1203 or the wiring line. Unlike a usual active matrix light emittingdevice, the cathode 1205 on the pixel is striped in the device of FIG.12 (similar to a cathode in a passive matrix device).

[0156]FIGS. 13A and 13B show the exterior of the active matrix lightemitting device illustrated in FIG. 11B. FIG. 13A is a top view thereofand FIG. 13B is a sectional view taken along the line P-P′ of FIG. 13A.The symbols in FIG. 11 are used in FIG. 13.

[0157] In FIG. 13A, 1301 denotes a pixel portion, 1302 denotes a gatesignal side driver circuit, and 1303 denotes a data signal side drivercircuit. Signals to be sent to the gate signal side driver circuit 1302and the data signal side driver circuit 1303 are inputted from a TAB(tape automated bonding) tape 1305 through an input wiring line 1304.Though not shown in the drawing, the TAB tape 1305 may be replaced by aTCP (tape carrier package) that is obtained by providing a TAB tape withan IC (integrated circuit).

[0158] Denoted by 1306 is the cover member that is provided in an upperpart of the organic light emitting device shown in FIG. 11B, and isbonded with a seal member 1307 formed of a resin. The cover member 1306may be any material as long as it does not transmit oxygen and water. Inthis embodiment, as shown in FIG. 13B, the cover member 1306 is composedof a plastic member 1306 a and carbon films (specifically, diamond-likecarbon films) 1306 b and 1306 c that are formed on the front and back ofthe plastic member 1306 a, respectively.

[0159] As shown in FIG. 13B, the seal member 1307 is covered with asealing member 1308 made of a resin so that the organic light emittingelement is completely sealed in an airtight space 1309. The airtightspace 1309 is filled with inert gas (typically, nitrogen gas or raregas), a resin, or inert liquid (for example, liquid fluorocarbon typicalexample of which is perfluoro alkane). It is also effective to put anabsorbent or deoxidant in the space.

[0160] A polarizing plate may be provided on a display face (the face onwhich an image is displayed to be observed by a viewer) of the lightemitting device shown in this embodiment. The polarizing plate has aneffect of reducing reflection of incident light from the external tothereby prevent the display face from showing the reflection of aviewer. Generally, a circular polarizing plate is employed. However, itis preferable for the polarizing plate to have a structure with lessinternal reflection by adjusting the index of refraction in order toprevent light emitted from the organic compound film from beingreflected at the polarizing plate and traveling backward.

[0161] Any of organic light emitting elements according to the presentinvention can be used as the organic light emitting element included inthe light emitting device of this embodiment.

Embodiment 5

[0162] This embodiment shows an active matrix light emitting device asan example of a light emitting device that includes an organic lightemitting element according to the present invention. Unlike Embodiment4, in the light emitting device of this embodiment. tight is taken outfrom the opposite side of a substrate on which an active element isformed (hereinafter referred to as upward emission). FIG. 14 is asectional view thereof.

[0163] A thin film transistor (hereinafter referred to as TFT) is usedhere as the active element, but the active element may be a MOStransistor. The TFT shown as an example is a top gate TFT (planar TFT,to be specific), but a bottom gate TFT (typically a reverse stagger TFT)may be used instead.

[0164] A substrate 1401, a current controlling TFT 1402 that is formedin a pixel portion, and a driver circuit 1412 of this embodiment havethe same structure as those of Embodiment 4.

[0165] A first electrode 1403, which is connected to a drain of thecurrent controlling TFT 1402, is used as an anode in this embodiment,and therefore is formed preferably from a conductive material having alarge work function. Typical examples of the conductive material includemetals such as nickel, palladium, tungsten, gold, and silver. In thisembodiment, the first electrode 1403 desirably does not transmit light.More desirably, the electrode is formed from a material that is highlyreflective of light.

[0166] On the first electrode 1403, an organic compound film 1404 isformed. Provided on the organic compound film 1404 is a second electrode1405, which serves as a cathode in this embodiment. Accordingly, thematerial of the second electrode 1405 is desirably a conductive materialhaving a work function of 2.5 to 3.5 eV. Typically, a conductive filmcontaining an alkaline metal element or an alkaline-earth metal element,or a conductive film containing aluminum, or a laminate obtained bylayering an aluminum or silver film on one of the above conductive filmsis used. However, being light-transmissive is indispensable for thematerial of the second electrode 1405. Therefore, when used for thesecond electrode, the metal is preferably formed into a very thin filmabout 20 nm in thickness.

[0167] A layer composed of the first electrode 1403, the organiccompound film 1404. and the second electrode 1405, are covered with aprotective film 1406. The protective film 1406 is provided to protectthe organic light emitting element from oxygen and moisture. In thisembodiment, any material can be used for the protective film as long asit transmits light.

[0168] The first electrode (anode) 1403 is electrically connected to thecurrent controlling TFT 1402 in FIG. 14 but the cathode may be connectedto the current controlling TFT instead. In this case, the firstelectrode is formed from the material of the cathode whereas the secondelectrode is formed from the material of the anode. The currentcontrolling TFT in this case is preferably an n-channel TFT.

[0169] Denoted by 1407 is a cover member and is bonded with a sealmember 1408 formed of a resin. The cover member 1407 may be any materialas long as it transmits light but not oxygen and water. In thisembodiment, glass is used. An airtight space 1409 is filled with inertgas (typically, nitrogen gas or rare gas), a resin, or inert liquid (forexample, liquid fluorocarbon typical example of which is perfluoroalkane). It is also effective to put an absorbent or deoxidant in thespace.

[0170] Signals to be sent to the gate signal side driver circuit and thedata signal side driver circuit are inputted from a TAB (tape automatedbonding) tape 1414 through an input wiring line 1413. Though not shownin the drawing, the TAB tape 1414 may be replaced by a TCP (tape carrierpackage) that is obtained by providing a TAB tape with an IC (integratedcircuit).

[0171] A polarizing plate may be provided on a display face (the face onwhich an image is displayed to be observed by a viewer) of the lightemitting device shown in this embodiment. The polarizing plate has aneffect of reducing reflection of incident light from the external tothereby prevent the display face from showing the reflection of aviewer. Generally, a circular polarizing plate is employed. However, itis preferable for the polarizing plate to have a structure with lessinternal reflection by adjusting the index of refraction in order toprevent light emitted from the organic compound film from beingreflected at the polarizing plate and traveling backward.

[0172] Any of organic light emitting elements according to the presentinvention can be used as the organic light emitting element included inthe light emitting device of this embodiment.

Embodiment 6

[0173] This embodiment shows a passive matrix light emitting device asan example of a light emitting device that includes an organic lightemitting element disclosed in the present invention. FIG. 15A is a topview thereof and FIG. 15B is a sectional view taken along the line P-P′of FIG. 15A.

[0174] In FIG. 15A, denoted by 1501 is a substrate, which is formed of aplastic material here. The plastic material, which can be used, is aplate or film of polyimide, polyamide, an acrylic resin, an epoxy resin,PES (polyethylene sulfile), PC (polycarbonate), PET (polyethyleneterephthalate), or PEN (polyethylene naphthalate).

[0175]1502 denotes scanning lines (anodes) formed from a conductiveoxide film. In this embodiment, the conductive oxide film is obtained bydoping zinc oxide with gallium oxide. 1503 denotes data lines (cathodes)formed from a metal film, a bismuth film, in this embodiment. 1504denotes banks formed of an acrylic resin. The banks function aspartition walls that separate the data lines 1503 from one another. Thescanning lines 1502 and the data lines 1503 respectively form stripepatterns and the patterns cross each other at right angles. Though notshown in FIG. 15A, an organic compound film is sandwiched between thescanning lines 1502 and the data lines 1503 and intersection portions1505 serve as pixels.

[0176] The scanning lines 1502 and the data lines 1503 are connected toan external driver circuit through a TAB tape 1507. 1508 denotes a groupof wiring lines comprised of a mass of the scanning lines 1502. 1509denotes a group of wiring lines comprised of a mass of connection wiringlines 1506 that are connected to the data lines 1503. Though not shown,the TAB tape 1507 may be replaced by TCP that is obtained by providing aTAB tape with an IC.

[0177] In FIG. 15B, 1510 denotes a seal member and 1511 denotes a covermember that is bonded to a plastic member 1501 with the seal member1510. A photo-curable resin can be used for the seal member 1510. Apreferable material of the seal member is one which allows little gasleakage and which absorbs little moisture. The cover member ispreferably made from the same material as the substrate 1501, and glass(including quartz glass) or plastic can be used. Here, a plasticmaterial is used for the cover member.

[0178]FIG. 15C is an enlarged view of the structure of a pixel region.1513 denotes an organic compound film. Lower layers of the banks 1504are narrower than upper layers and therefore the banks can physicallyseparate the data lines 1503 from one another. A pixel portion 1514surrounded by the seal member 1510 is shut off of the outside air by asealing member 1515 formed of a resin. Degradation of the organiccompound film is thus prevented.

[0179] In the light emitting device structured as above in accordancewith the present invention, the pixel portion 1514 is composed of thescanning lines 1502, the data lines 1503, the banks 1504, and theorganic compound film 1513. Therefore the light emitting device can bemanufactured by a very simple process.

[0180] A polarizing plate may be provided on a display face (the face onwhich an image is displayed to be observed by a viewer) of the lightemitting device shown in this embodiment. The polarizing plate has aneffect of reducing reflection of incident light from the external tothereby prevent the display face from showing the reflection of aviewer. Generally, a circular polarizing plate is employed. However, itis preferable for the polarizing plate to have a structure with lessinternal reflection by adjusting the index of refraction in order toprevent light emitted from the organic compound film from beingreflected at the polarizing plate and traveling backward.

[0181] Any of organic light emitting elements according to the presentinvention can be used as the organic light emitting element included inthe light emitting device of this embodiment.

Embodiment 7

[0182] This embodiments shows an example of attaching a printed wiringboard to the light emitting device shown in Embodiment 6 to make thedevice into a module.

[0183] In a module shown in FIG. 16A, a TAB tape 1604 is attached to asubstrate 1601 (here including a pixel portion 1602 and wiring lines1603 a and 1603 b), and a printed wiring board 1605 is attached to thesubstrate through the TAB tape 1604.

[0184] A functional block diagram of the printed wiring board 1605 isshown in FIG. 16B. An IC functioning as at least I/O ports (input oroutput portions) 1606 and 1609, a data signal side driver circuit 1607,and a gate signal side driver circuit 1608 are provided within theprinted wiring board 1605.

[0185] In this specification, a module structured by attaching a TABtape to a substrate with a pixel portion formed on its surface and byattaching a printed wiring board that functions as a driver circuit tothe substrate through the TAB tape as above is specially named a modulewith external driver circuit.

[0186] Any of organic light emitting elements disclosed in the presentinvention can be used as the organic light emitting element included inthe light emitting device of this embodiment.

Embodiment 8

[0187] This embodiment shows an example of attaching a printed wiringboard to the light emitting device shown in Embodiment 4, 5, or 6 tomake the device into a module.

[0188] In a module shown in FIG. 17A, a TAB tape 1705 is attached to asubstrate 1701 (here including a pixel portion 1702, a data signal sidedriver circuit 1703. a gate signal side driver circuit 1704, and wiringlines 1703 a and 1704 a), and a printed wiring board 1706 is attached tothe substrate through the TAB tape 1705. A functional block diagram ofthe printed wiring board 1706 is shown in FIG. 17B.

[0189] As shown in FIG. 17B, an IC functioning as at least I/O ports1707 and 1710 and a control unit 1708 is provided within the printedwiring board 1706. A memory unit 1709 is provided here but it is notalways necessary. The control unit 1708 is a portion having functionsfor controlling the driver circuits and correction of image data.

[0190] In this specification, a module structured by attaching a printedwiring board that has functions as a controller to a substrate on whichan organic light emitting element is formed as above is specially nameda module with external controller.

[0191] Any of organic light emitting elements disclosed in the presentinvention can be used as the organic light emitting element included inthe light emitting device of this embodiment.

Embodiment 9

[0192] This embodiment shows an example of light emitting device inwhich a triplet light emitting element shown in Embodiment 3 is drivenin accordance with digital time gray scale display. The light emittingdevice of this embodiment can provide uniform images in digital timegray scale display by using a light emitting from the state of tripletexcitation and therefore is very useful. It should be noted that thedriving method of the present invention is not limited to thisembodiment and other known methods may be used.

[0193]FIG. 18A shows the circuit structure of a pixel that uses anorganic light emitting element. Tr represents a transistor and Csrepresents a storage capacitor. In the circuit configuration of FIG.18C, the source line is connected to the source of the transistor Tr1,and the gate line is connected to the gate of the transistor Tr1. Also,the power supply time is connected to the storage capacitor Cs and thesource of the transistor Tr2. Since the anode of the organic lightemitting, element of the present invention is connected to the drain ofthe transistor Tr2, the cathode is on the opposite side of thetransistor Tr2 with the organic light emitting element interposedtherebetween. In this circuit, when a gate line is selected, a currentflows into Tr1 from a source line and a voltage corresponding to thesignal is accumulated in Cs. Then a current controlled by thegate-source voltage (V_(gs)) of Tr2 flows into Tr2 and the organic lightemitting element.

[0194] After Tr1 is selected, Tr1 is turned OFF to hold the voltage(V_(gs)) of Cs. Accordingly a current continues to flow in an amountdependent of V_(gs).

[0195]FIG. 18B shows a chart for driving this circuit in accordance withdigital time gray scale display. In digital time gray scale display, oneframe is divided into plural sub-frames. FIG. 15B shows 6 bit gray scalein which one frame is divided into six sub-frames. (SF1-SF6) TA is thewriting time. In this case, the ratio of light emission periods of thesub-frames is 32:16:8:4:2:1 as shown in the figure.

[0196]FIG. 18C schematically shows driver circuits of TFT substrate inthis embodiment. In the substrate configuration of FIG. 18C, the powersupply line and the cathode as shown in FIG. 18A are connected to thepixels of the light emitting element. Also, the shift register isconnected to the pixel portion in the order of from the shift register,the latch 1, the latch 2 and the pixel portion. The latch 1 is inputwith digital signal and image signals can be transferred to the pixelportion by the latch pulses input to the latch 2. A gate driver and asource driver are provided on the same substrate, and the pixel circuitand the drivers are designed to be digitally driven. Accordingly,fluctuation in TFT characteristic does not affect the device and thedevice can display uniform images.

Embodiment 10

[0197] In this embodiment, an example of an active matrix typeconstant-current driver circuit is described, which is driven by flowingthe constant current in the organic light emitting element of thepresent invention. The circuit structure thereof is shown in FIG. 21.

[0198] The pixel 2110 shown in FIG. 21 has the signal line Si, the firstscanning line Gj, the second scanning line Pj and the power source lineVi. In addition, the pixel 2110 has Tr1, Tr2, Tr3, Tr4, the organiclight emitting element 2111 of a mixed junction type and the retentioncapacitor 2112.

[0199] Both gates of Tr3 and Tr4 are connected with the first scanningline Gj. As for the source and the drain of Tr3, the one is connectedwith the signal line Si, the other is connected with the source of Tr2.Further, the source and the drain of Tr4, the one is connected with thesource of Tr2, the other is connected to the gate of Tr1. Thus, theeither of the source and the drain of Tr3 and the either of the sourceor the drain of Tr4 are connected with each other.

[0200] The source of Tr1 is connected with the power source line Vi, thedrain is connected with the source of Tr2. The gate of Tr2 is connectedto the second scanning line Pj. And, the drain of the Tr2 is connectedwith a pixel electrode in the organic light emitting element 2111. Theorganic light emitting element 2111 has the pixel electrode, the counterelectrode and the organic light emitting layer provided between thepixel electrode and the counter electrode. The counter electrode of theorganic light emitting element 2111 is applied constant voltage by apower source provided at the external of a light emitting panel.

[0201] Tr3 and Tr4 can adopt both n-channel type TFT and p-channel typeTFT. However, the polarities of Tr3 and Tr4 are the same. Further, Tr1can adopt both n-channel type TFT and p-channel type TFT. Tr2 can adoptboth n-channel type TFT and p-channel type TFT. With respect to thepolarity, in the case of the pixel electrode of the light emittingelectrode and the counter electrode, the one is an anode, the other is acathode. In the case that the Tr2 is a p-channel type TFT, it ispreferable to use the anode as a pixel electrode, and the cathode as acounter electrode. On the other hand, in the case that the Tr2 is ann-channel type TFT. it is preferable to use the cathode as a pixelelectrode, and the anode as a counter electrode.

[0202] The retention capacitor 2112 is formed between the gate and thesource of Tr1. The retention capacitor 2112 is provided to maintain morecertainly the voltage (V_(GS)) between the gate and the source of Tr1.However, it is not necessary always provided.

[0203] In the pixel shown in FIG. 21, the current supplied to the signalline Si is controlled at the current source in the signal line drivercircuit.

[0204] By applying the above-mentioned circuit structure, theconstant-current driving can be realized, by which the brightness can bekept by flowing a constant current in the organic light emittingelement. The organic light emitting element having a mixture region ofthe present invention has a longer lifetime than that of prior organiclight emitting element. The organic light emitting element is effectivebecause longer lifetime can be realized by implementing above-mentionedconstant-current driving.

Embodiment 11

[0205] The light emitting devices of the present invention, which havebeen described in, the embodiments above have advantages of low powerconsumption and long lifetime. Accordingly, electric appliances thatinclude those light emitting devices as their display portions canoperate consuming less power than conventional ones and are durable. Theadvantages are very useful especially for electric appliances that usebatteries as power sources, such as portable equipment, because lowpower consumption leads directly to conveniences (batteries lastlonger).

[0206] The light emitting device is self-luminous to eliminate the needfor back light as the one in liquid crystal displays, and has an organiccompound film whose thickness is less than 1 μm. Therefore the lightemitting device can be made thin and light-weight. Electric appliancesthat include the light emitting device as their display portions areaccordingly thinner and lighter than conventional ones. This too leadsdirectly to conveniences (lightness and compactness in carrying themaround) and is very useful particularly for portable equipment and likeother electric appliances. Moreover, being thin (unvoluminous) isdoubtlessly useful for all of the electric appliances in terms oftransportation (a large number of appliances can be transported in amass) and installation (space-saving).

[0207] Being self-luminous, the light emitting device is characterizedby having better visibility in bright places than liquid crystal displaydevices and wide viewing angle. Therefore electric appliances thatinclude the light emitting device as their display portions areadvantageous also in terms of easiness in viewing display.

[0208] To summarize, electric appliances that use a light emittingdevice of the present invention have, in addition to merits ofconventional organic light emitting elements, namely, thinness/lightnessand high visibility, new features of low power consumption and longlifetime, and therefore are very useful.

[0209] This embodiment shows examples of the electric appliances thatinclude as display portions the light emitting device of the presentinvention. Specific examples thereof are shown in FIGS. 19A and 20B. Anyelements disclosed in the present invention can be used for the organiclight emitting element included in the electric appliance of thisembodiment. The light emitting device included in the electric applianceof this embodiment can have any of the configurations illustrated inFIGS. 11 to 18.

[0210]FIG. 19A shows a display device using an organic light emittingelement. The display is composed of a case 1901 a, a support base 1902a, and a display portion 1903 a. By using a light emitting device of thepresent invention as the display portion 1903 a, the display can be thinand light-weight, as well as durable. Accordingly, transportation issimplified, space is saved in installation, and lifetime is long.

[0211]FIG. 19B shows a video camera, which is composed of a main body1901 b, a display portion 1902 b, an audio input portion 1903 b,operation switches 1904 b, a battery 1905 b, and an image receivingportion 1906 b. By using a light emitting device of the presentinvention as the display portion 1902 b, the video camera can be thinand light-weight, and consumes less power. Accordingly, batteryconsumption is reduced and carrying the video camera is lessinconvenient.

[0212]FIG. 19C shows a digital camera, which is composed of a main body1901 c, a display portion 1902 c, an eye piece portion 1903 c, andoperation switches 1904 c. By using a light emitting device of thepresent invention as the display portion 1902 c, the digital camera canbe thin and light-weight, and consumes less power. Accordingly, batteryconsumption is reduced and carrying the digital camera is lessinconvenient.

[0213]FIG. 19D shows an image reproducing device equipped with arecording medium. The device is composed of a main body 1901 d, arecording medium (such as CD, LD, or DVD) 1902 d, operation switches1903 d, a display portion (A) 1904 d, and a display portion (B) 1905 d.The display portion (A) 1904 d mainly displays image information whereasthe display portion (B) 1905 d mainly displays text information. Byusing a light emitting device of the present invention as the displayportion (A) 1904 d and the display portion (B) 1905 d, the imagereproducing device consumes less power and can be thin and light-weightas well as durable. The image reproducing device equipped with arecording medium also includes CD players and game machines.

[0214]FIG. 19E shows a (portable) mobile computer, which is composed ofa main body 1901 e, a display portion 1902 e, an image receiving portion1903 e, a switch 1904 e, and a memory slot 1905 e. By using a lightemitting device of the present invention as the display portion 1902 e.the portable computer can be thin and light-weight, and consumes lesspower. Accordingly, battery consumption is reduced and carrying thecomputer is less inconvenient. The portable computer can storeinformation in a flash memory or a recording medium obtained byintegrating non-volatile memories and can reproduce the storedinformation.

[0215]FIG. 19F shows a personal computer, which is composed of a mainbody 1901 f, a case 1902 f, a display portion 1903 f, and a keyboard1904 f. By using a light emitting device of the present invention as thedisplay portion 1903 f, the personal computer can be thin andlight-weight, and consumes less power. The light emitting device is agreat merit in terms of battery consumption and lightness especially fora notebook personal computer or other personal computers that arecarried around.

[0216] These electric appliances now display with increasing frequencyinformation sent through electronic communication lines such as theInternet and radio communications such as radio wave, especially,animation information. Since organic light emitting elements have veryfast response speed, the light emitting device is suitable for animationdisplay.

[0217]FIG. 20A shows a cellular phone, which is composed of a main body2001 a, an audio output portion 2002 a, an audio input portion 2003 a, adisplay portion 2004 a, operation switches 2005 a, and an antenna 2006a. By using a light emitting device of the present invention as thedisplay portion 2004 a, the cellular phone can be thin and light-weight,and consumes less power. Accordingly, battery consumption is reduced,carrying the cellular phone is easy, and the main body is compact.

[0218]FIG. 20B shows audio (specifically, car audio), which is composedof a main body 2001 b, a display portion 2002 b, and operation switches2003 b and 2004 b. By using a light emitting device of the presentinvention as the display portion 2002 b, the audio can be thin andlight-weight, and consumes less power. Although car audio is taken as anexample in this embodiment. the audio may be home audio.

[0219] It is effective to give the electric appliances shown in FIGS.19A to 20B a function of modulating the luminance of emitted light inaccordance with the brightness of the surroundings where the electricappliances are used by providing the electric appliances with photosensors as measures to detect the brightness of the surroundings. A usercan recognize image or text information without difficulties if thecontrast ratio of the luminance of emitted light to the brightness ofthe surroundings is 100 to 150. With this function, the luminance of animage can be raised for better viewing when the surroundings are brightwhereas the luminance of an image can be lowered to reduce powerconsumption when the surroundings are dark.

[0220] Various electric appliances that employ as light sources thelight emitting device of the present invention are also thin andlight-weight and can operate consuming less power. which makes them veryuseful appliances. Light sources of liquid crystal display devices, suchas back light or front light, or light sources of lighting fixtures aretypical uses of the light emitting device of the present invention as alight source.

[0221] When liquid crystal displays are used as the display portions ofthe electric appliances shown in FIGS. 19A to 20B according to thisembodiment, the electric appliances can be thin and light-weight andconsume less power if those liquid crystal displays use as back light orfront light the light emitting device of the present invention.

[0222] A light emitting device having low electric power consumption andsuperior longevity can be obtained by implementing the presentinvention. In addition, electronic devices which are bright, have lowelectric power consumption, and a long life can be obtained by usingthis type of light emitting device as a light source or as a displayportion.

[0223] In the preferred embodiments of the present invention, theconcentration changing regions are disposed between the holetransportation region and the mixture region and between the electrontransportation region and the mixture region, respectively. However, thepresent invention may include a light emitting device in which only oneconcentration changing region is disposed between the mixture region anddesired one of the hole transportation region and the electrontransportation region.

What is claimed is:
 1. A light emitting device comprising an organiclight emitting element, the organic light element having: an anode; acathode; an organic compound film containing a hole transportingmaterial and an electron transporting material; wherein the organiccompound film has a structure which comprises in a direction from theanode to the cathode: a hole transporting region made from the holetransporting material; a first concentration change region in which theproportion of the electron transporting material increases graduallyuntil a ratio between the hole transporting material and the electrontransporting material becomes x:y (where x and y are positiveconstants); a mixture region containing the hole transporting materialand the electron transporting material at the ratio of x: y; a secondconcentration change region in which the proportion of the electrontransporting material gradually increases further from the x:y ratio;and an electron transporting region made from the electron transportingmaterial; and wherein a light emitting region, into which a lightemitting material for performing light emission is added, is formedwithin the mixture region.
 2. A light emitting device comprising anorganic light emitting element, the organic light element having: ananode; a cathode; a hole injecting region formed contacting the anode;an organic compound film containing a hole transporting material and anelectron transporting material; wherein the organic compound film has astructure which comprises in a direction from the anode to the cathode:a hole transporting region made from the hole transporting material: afirst concentration change region in which the proportion of theelectron transporting material increases gradually until a ratio betweenthe hole transporting material and the electron transporting materialbecomes x:y (where x and y are positive constants); a mixture regioncontaining the hole transporting material and the electron transportingmaterial at the ratio of x:y; a second concentration change region inwhich the proportion of the electron transporting material graduallyincreases further from the x:y ratio; and an electron transportingregion made from the electron transporting material; wherein a lightemitting region, into which a light emitting material for performinglight emission is added, is formed within the mixture region.
 3. A lightemitting device comprising an organic light emitting element, theorganic light element having: an anode; a cathode; an electron injectingregion formed contacting the cathode; and an organic compound filmcontaining a hole transporting material and an electron transportingmaterial, wherein the organic compound film has a structure whichcomprises in a direction from the anode to the cathode: a holetransporting region made from the hole transporting material: a firstconcentration change region in which the proportion of the electrontransporting material increases gradually until a ratio between the holetransporting material and the electron transporting material becomes x:y(where x and y are positive constants); a mixture region containing thehole transporting material and the electron transporting material at theratio of x:y; a second concentration change region in which theproportion of the electron transporting material gradually increasesfurther from the x:y ratio; and an electron transporting region madefrom the electron transporting material; and wherein a light emittingregion, into which a light emitting material for performing lightemission is added, is formed within the mixture region.
 4. A lightemitting device comprising an organic light emitting element, theorganic light element comprising: an anode; a cathode; a hole injectingregion formed contacting the anode; an electron injecting region formedcontacting the cathode; and an organic compound film containing a holetransporting material and an electron transporting material; wherein theorganic compound film has a structure which comprises in a directionfrom the anode to the cathode: a hole transporting region made from thehole transporting material; a first concentration change region in whichthe proportion of the electron transporting material increases graduallyuntil a ratio between the hole transporting material and the electrontransporting material becomes x:y (where x and y are positiveconstants); a mixture region containing the hole transporting materialand the electron transporting material at the ratio of x:y; a secondconcentration change region in which the proportion of the electrontransporting material gradually increases further from the x:y ratio;and an electron transporting region made from the electron transportingmaterial, and wherein a light emitting region, into which a lightemitting material for performing light emission is added, is formedwithin the mixture region.
 5. A light emitting device according to anyone of claims 1 to 4, wherein the light emitting region, into which thelight emitting material is added, is a portion within the mixtureregion.
 6. A light emitting device according to any one of claims 1 to4, wherein a blocking material, having an energy difference between itshighest occupied molecular orbital and its lowest unoccupied molecularorbital which is larger than that of the hole transporting material andthe electron transporting material, is added to a portion within themixture region.
 7. A light emitting device according to claim 5,wherein: a blocking material, having an energy difference between itshighest occupied molecular orbital and its lowest unoccupied molecularorbital which is larger than that of the hole transporting material andthe electron transporting material, is added to a portion within themixture region; and the light emitting region having the light emittingmaterial added thereto is positioned closer to the anode than to theregion having the blocking material added thereto.
 8. A light emittingdevice according to any one of claims 1 to 4, wherein the light emittingmaterial performs light emission from a triplet excitation state.
 9. Alight emitting device according to any one of claims 1 to 4, whereinmass percentage of the hole transporting material within the mixtureregion is greater than or equal to 10%, and less than or equal to 90%,with respect to total mass of the hole transporting material and theelectron transporting material.
 10. The light emitting device accordingto any one of claims 1 to 4, wherein the mixture region has a thicknessgreater than or equal to 10 nanometers, and less than or equal to 100nanometers.
 11. An electronic device using the light emitting deviceaccording to any one of claims 1 to
 4. 12. The light emitting deviceaccording to any one of claims 1 to 4 wherein the light emitting deviceis a passive matrix type.
 13. The light emitting device according to anyone of claims 1 to 4 wherein the light emitting device is an activematrix type.
 14. A light emitting device comprising: an anode; acathode; and an organic compound film containing a hole transportingmaterial and an electron transporting material, the organic compoundfilm comprising: a hole transporting region comprising the holetransporting material adjacent to the anode; an electron transportingregion comprising the electron transporting material adjacent to thecathode; a mixture region disposed between the hole transporting regionand the electron transporting region and comprising the holetransporting material and the electron transporting material at aconstant proportion in a direction along the anode and the cathode,wherein the mixture region is doped with a light emitting material atleast partly; a first concentration changing region disposed between thehole transporting region and the mixture region wherein the proportionof the electron transporting material relative to the hole transportingmaterial monotonically increases in the first concentration changingregion in a direction from the hole transporting region to the mixtureregion; and a second concentration changing region disposed between themixture region and the electron transporting region wherein theproportion of the electron transporting material relative to the holetransporting material monotonically increases in the secondconcentration changing region in a direction from the mixture region tothe electron transporting region.
 15. The light emitting deviceaccording to claim 14 wherein said light emitting device is a passivematrix type.
 16. The light emitting device according to claim 14 whereinsaid light emitting device is an active matrix type.
 17. An electronicdevice comprising the light emitting device according to claim 14wherein said electronic device is one selected from the group consistingof a video camera, digital camera, an image reproducing device, a mobilecomputer, a personal computer, a cellular phone, and an audio.
 18. Alight emitting device comprising: an anode; a cathode; and an organiccompound film containing a hole transporting material and an electrontransporting material, the organic compound film comprising: a holetransporting region comprising the hole transporting material adjacentto the anode; an electron transporting region comprising the electrontransporting material adjacent to the cathode; a mixture region disposedbetween the hole transporting region and the electron transportingregion and comprising the hole transporting material and the electrontransporting material at a constant proportion in a direction along theanode and the cathode, wherein the mixture region is doped with a lightemitting material at least partly; a concentration changing regiondisposed between the hole transporting region and the mixture regionwherein the proportion of the electron transporting material relative tothe hole transporting material monotonically increases in the firstconcentration changing region in a direction from the hole transportingregion to the mixture region.
 19. The light emitting device according toclaim 14 wherein said light emitting device is a passive matrix type.20. The light emitting device according to claim 14 wherein said lightemitting device is an active matrix type.
 21. An electronic devicecomprising the light emitting device according to claim 14 wherein saidelectronic device is one selected from the group consisting of a videocamera, digital camera, an image reproducing device, a mobile computer,a personal computer, a cellular phone, and an audio.
 22. A lightemitting device comprising: an anode; a cathode; and an organic compoundfilm containing a hole transporting material and an electrontransporting material, the organic compound film comprising: a holetransporting region comprising the hole transporting material adjacentto the anode; an electron transporting region comprising the electrontransporting material adjacent to the cathode; a mixture region disposedbetween the hole transporting region and the electron transportingregion and comprising the hole transporting material and the electrontransporting material at a constant proportion in a direction along theanode and the cathode, wherein the mixture region is doped with a lightemitting material at least partly; and a concentration changing regiondisposed between the mixture region and the electron transporting regionwherein the proportion of the electron transporting material relative tothe hole transporting material monotonically increases in the secondconcentration changing region in a direction from the mixture region tothe electron transporting region.
 23. The light emitting deviceaccording to claim 22 wherein said light emitting device is a passivematrix type.
 24. The light emitting device according to claim 22 whereinsaid light emitting device is an active matrix type.
 25. An electronicdevice comprising the light emitting device according to claim 22wherein said electronic device is one selected from the group consistingof a video camera, digital camera, an image reproducing device, a mobilecomputer, a personal computer, a cellular phone, and an audio.